Method to minimize the amount of oil in the air exhausted from a pneumatically operated impact motor and an impact motor for carrying out this method

Abstract

An impact motor has a reciprocating piston that has its piston rod guided in bushings in the housing. The bushings are lubricated by oil-loaded compressed air but the piston is forced to reciprocate by oil-free compressed air.

What we claim is: 
     
       1. Method to minimize the amount of oil in the air exhausted from a pneumatically operated impact motor comprising: mounting a hammer piston having an interconnected drive head and piston rod in a housing having a drive chamber such that the drive head is reciprocably mounted in the drive chamber with a clearance between the drive head and the inner wall of the drive chamber, said piston rod extending out of the drive chamber in at least one direction;   passing said piston rod through at least one guide portion in said housing with a clearance therebetween for guiding said hammer piston in its reciprocatory movement;   maintaining said drive head of said piston out of direct contact with the wall of the drive chamber by dimensioning said piston rod and said at least one guide portion such that said clearance between said piston rod and said at least one guide portion is smaller than said clearance between said drive head and the wall of the drive chamber;   supplying said drive chamber with substantially oil-free compressed air for actuating the hammer piston;   supplying lubricant to said at least one guide portion; and   substantially blocking lubricant flow from said at least one guide portion to said drive chamber so as to maintain the air in said drive chamber substantially lubricant free.   
     
     
       2. Method according to claim 1 wherein said lubricant supplied to said at least one guide portion is carried by compressed air. 
     
     
       3. Method according to claim 2 comprising supplying the lubricant-carrying compressed air to an air distributing valve which is separate from the hammer piston to shift the position of the valve. 
     
     
       4. Method according to claim 2 comprising supplying the lubricant-carrying compressed air to an air distributing valve which is separate from the hammer piston to lubricate the valve. 
     
     
       5. Pneumatically operated impact motor, comprising: a housing with a drive chamber therein;   a hammer piston having a drive head which is reciprocably mounted in said drive chamber with a clearance between said drive head and the wall of said drive chamber, said hammer piston comprising a piston rod that extends out of the drive chamber;   said housing comprising at least one guide portion for guiding the piston rod with a clearance between said at least one guide portion and said piston rod;   said piston rod and said at least one guide portion being dimensioned such that said clearance between the piston rod and said at least one guide portion is smaller than said clearance between the piston head and the wall of the drive chamber to prevent direct contact between the piston head and the wall of the drive chamber;   passage means for supplying a lubricant to said at least one guide portion for guiding the piston rod;   means for supplying substantially oil-free compressed motive fluid to said drive chamber to actuate said hammer piston; and   means for substantially blocking lubricant flow from said at least one guide portion to said drive chamber.   
     
     
       6. Impact motor according to claim 5, wherein said hammer piston has a further piston rod which extends out of the drive chamber in a direction opposite to that of the first-mentioned piston rod, and wherein the housing has a further guide portion cooperating with said further piston rod with a clearance therebetween, said clearance between said further piston rod and said further guide portion being smaller than said clearance between the piston head and the wall of the drive chamber. 
     
     
       7. Impact motor according to claim 6 comprising a distributing valve for the motive fluid, said valve being separate from the hammer piston, and passages for supplying a lubricant to the valve, said passages for supplying lubricant to the valve and to said at least one guide portion being connected to a common supply passage for oil-loaded compressed air. 
     
     
       8. Impact motor according to claim 6 comprising a separate distributing valve for the motive fluid, and a control circuit air coupled to the distributing valve to shift the position of the distributing valve, said control circuit air being separate from the means for supplying said motive fluid. 
     
     
       9. Impact motor according to claim 5 wherein said means for supplying said motive fluid comprises means for supplying compressed air, said impact motor further comprising a separate distributing valve for the compressed air, and a circuit for control air coupled to the separate compressed air distributing valve to shift the position of the separate compressed air distributing valve, said circuit for control air being separate from said means for supplying said compressed air. 
     
     
       10. Impact motor according to claim 5 wherein said motive fluid is compressed air, and comprising a distributing valve for the compressed air, said distributing valve being separate from the hammer piston, and passages for supplying a lubricant to the distributing valve, said passages for supplying lubricant to the distributing valve and to said at least one guide portion being connected to a common supply passage for oil-loaded compressed air. 
     
     
       11. Impact motor according to claim 5 wherein said motive fluid is compressed air.